Advanced Marine Electrics and Electronics Troubleshooting A Manual for Boatowners and Marine Technicians

As we saw above, frequency matters, and
on your transistor radio, the AM band you are
listening to is in the 540 kHz to 1,700 kHz
range. If you switch to the FM band and use
the same technique, you will be listening in
the 88 MHz to 108 MHz range.
You’ll only encounter interference prob-
lems when the interfering frequency is fairly
close to the frequency at which a given device
operates. What frequencies do boat appliances
run at? Table 9-1 lists the operating frequencies
of some common marine electronic devices.
The frequency range of the radio is close
enough to the frequencies of most onboard
electronics to reveal interference problems.
Once you’ve figured out where the inter-
ference is coming from, turn to Chapter 12 to
find out how to minimize its effects.

Gauss Meter

The gauss meter is used in almost exactly the
same way as the transistor radio, except that
instead of listening to the interference, you get
a numerical readout in milligauss (mG). For
the meter to measure the magnetic field
strength accurately, the device being measured
must be pulling full current. As you move the
meter closer to a device, the readings will

testing for electromagnetic and radio frequency interference 91

To establish a safe RFI separation distance or zone from
an alternator, move the radio around until the radio static
peaks. Then gradually move the radio away from that
point until you no longer hear static. This is the minimum
separation distance.

Electronic Equipment Frequency

Cell phone 850 MHz or 1.96 GHz

Depth sounder 50 or 200 kHz

Differential GPS 150—500 kHZ

GPS 1.5 GHz

Loran-C 90—110 kHz

AM radio receiver 540—1,700 kHz

FM radio receiver 88—108 MHz

SSB radio 2—22 MHz

VHF radio 160 MHz

Operating Frequencies of

Common Onboard Electronics

TABLE

9-1

This Sperry gauss meter has a range of 0.1 to 199.9 mG.